PROJECT SUMMARY/ABSTRACT Aging is associated with a gradual decline in cognitive function, which can affect quality of life and predisposes individuals to age-related neurodegenerative diseases, including Alzheimer?s disease and its related dementias (ADRD). As the population of mid-life and older adults is increasing rapidly, there is increasing need to understand the mechanisms of cognitive aging. Studies in mid-life individuals are particularly important as interventions are needed to help prevent factors that contribute to cognitive decline and risk of ADRD. Passive heat therapy?repeated chronic use of hot baths and saunas?has been used for centuries with common reports of improved overall health and well-being, but has only recently gained attention for its potential utility in preventing cardiovascular disease (CVD). Recently, a 30-year prospective cohort study in middle-aged Finnish men found that increased frequency or session duration of habitual sauna bathing was associated with reduced risk of sudden cardiac and CVD-related death, as well as ~50% reduced risk of incident hypertension. Importantly, this group also reported that the frequency of sauna bathing was associated with lowered risks of dementia and Alzheimer's disease. The results of these studies suggest that heat therapy may reduce the risk of hypertension and dementia through reductions in systolic blood pressure, improvements in arterial stiffness and endothelial function, or through alternative, independent means. However, this has never been investigated via a randomized clinical research trial. Therefore, the purpose of this administrative supplement is to compare the benefits of heat therapy to exercise training in middle-aged individuals with hypertension on cognitive function and MRI-based markers of ADRD risk. These studies will be performed in study participants aged 50-64 years with elevated blood pressure or Stage-1 hypertension. We aim to determine whether 30 sessions of heat therapy or exercise training improves cognitive function (using the NIH Toolbox) and MRI-based markers of aging and Alzheimer?s risk (using specific MRI-based biomarkers and tests). These studies in mid-life adults will determine if heat therapy can be used to improve cognitive aging and dementia risk, with potentially important clinical implications for the prevention of ADRD.